User agent devices can function as end-points of a communication session. A communication session can include a voice communication session, such a voice call, or a data communication session, such as a video call. A user agent device can comprise a telephone within the public switched telephone network (PSTN), a cellular phone within a cellular radio access network (RAN), a phone within a packet-switched network, such as a session initiation protocol (SIP) phone, or some other type of phone or device.
From a perspective of a user agent device that initiates a communication session, that user agent device can be referred to as a near-end device, whereas a user agent device at the other end of the communication session can be referred to as a far-end device. From a perspective of the called user agent device, that user agent device can be referred to as the near-end device, whereas the user agent device that initiated the communication session can be referred to as the far-end device.
User agent devices can carry out the communication sessions using a communications network that includes or accesses a domain name system (DNS) of the Internet. The communications network can be referred to as a packet-switched network. A packet-switched network can carry data, such as voice data, using packets of data. The packet-switched network is not necessarily dedicated to a single communication session. Portions of a communication session, such as portions of the communication session transmitted to and from a user agent device can be carried out using a circuit-switched network. A portion of the circuit-switched network can be dedicated to the user agent devices carrying out a communication signal.
Unless otherwise indicated herein, the elements described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.